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The classic for measuring axial displacement in boreholes

Extensometers are among the most frequently used instruments for measuring the axial deformation along a borehole. They are used for monitoring support and anchoring systems in slope protections, open cuts, underground constructions etc. or to observe settlement and sliding. Several single extensometers can be bundled into multiple extensometers with anchoring points in different depths. This way, it is possible to identify the areas where movement has occurred. The magnitude and progression over time of these movements are valuable indicators for assessing stabilizing measures and help specify the necessary anchor length.

Principle of operation

The anchor part is firmly fixed in the borehole and is connected to the measuring rod, which transfers the movements up to a measuring stop in the reference head, which is attached to the mouth of the borehole. Thus, a relative movement between anchor part and borehole mouth via measuring the distance between measuring head and measuring stop can be recorded. The rod is isolated from the backfill material in the borehole by a protective tube and therefore guarantees its free movement. Depending on the rock mass properties, the anchor part can either be fixed by fully grouting of the entire borehole or by the use of packer anchors. In the latter case, only those anchor parts equipped with a fleece packer are injected 
The measuring stop can be adjusted by means of a simple to adapt the measuring range accordingly. Reading is done either manually with a dial depth gauge or by means of a portable electric reading device when using electrical displacement transducers. Retrofitting with displacement transducers is also possible at a later time. The use of displacement transducers also enables remote reading and automated data acquisition by means of a data logger and/or radio data transmission.

Tailor-made variants

Depending on the measuring task and ambient conditions, different versions are possible. For fractured rock, our packer anchor parts can be used to prevent the loss of injection material and ensure a frictional connection with the borehole wall. The measuring heads are designed to be equipped with electrical displacement transducers – even at a later date. Numerous variants with different measuring paths up to pressure watertight models are also available for this purpose. 

The measuring rods usually consist of corrosion-resistant GRP rods with a diameter of 10 mm. In combination with the PVC cladding tube, it is possible to easily adapt the lengths to the conditions immediately before installation on site. If required, galvanised steel or stainless steel can also be supplied.

Our services

We deliver all components in the desired design. Our technicians are also happy to carry out the installation on site. If an automatic measurement data acquisition is desired, we plan and deliver optimized solutions and accompany our customers until commissioning.


  • Suitable for installation lengths of more than 100 m
  • A combination of up to 6 single extensometer in one borehole is possible
  • Any installation direction applicable
  • Large measuring range due to adjustable measuring stop
  • Manual reading with dial gauge or electrically with displacement transducers

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